The two categories of electro-mechanical pumps namely; force and compression pumps all require moving parts for proper operation and in some special way these parts are designed in relation to the amount of fluid to be pumped per unit time and further the overall volume of the physical pump design. Compression pumps known as positive displacement types are capable of generating great pressure, nevertheless requires many moving parts such as a piston, piston rod, crankshaft, and associated valve assemblies. Positive displacement constriction pumps are the safest; mainly because the pumped fluid never contacts an n environment different than its internal tubing. They are for this fact used widely in the medical and pharmaceutical sector where the prevention of contamination is a vital factor. Their major disadvantage lies in the possible crushing forces upon the material being pumped if the tubing constricts completely. The moving parts required therein wear out from the fatigue caused by continuous operation. There is for consideration the operation of prior art relating to sonic and ultrasonic pumps that feature as an embodiment using acoustic standing waves for their principle of operation. Specific references are to the patents of: Mandroian U.S. Pat. No. 3,743,446, Lucas U.S. Pat. No. 5,020,977, Lucas U.S. Pat. No. 5,263,341, and Deak U.S. Pat. No. 5,525,041. Referring to the Mandroian patent, it uses a source of sound from a fluctuating diaphragm or piezoelectric transducer that oscillates at a preselected frequency. The frequency of oscillation of the diaphragm piezoelectric transducer and the length of the pump chamber are configured together so that this arrangement forms a resonant cavity (chamber) where acoustic standing waves are established in the fluids which allows for a pressure node or antinode at the wall opposite the diaphragm piezoelectric transducer. A series of pressure nodes and antinodes are distributed along the length of the chamber, and the number of nodes and antinodes depending upon the length of the chamber and the frequency of vibration of the diaphragm piezoelectric transducer. Mandroian further describes that the entrance port for the fluid is located in the chamber at one of the pressure nodes and an exit port is located at one of the pressure antinodes. This embodiment requires that a resonant condition must be created before any pumping action occurs and further, it is critical to have the dimensions of the chamber such that the entrance and exit ports are precisely on the nodes and antinodes for proper operation. This proper operation relies heavily on frequency resonant conditions within the chamber; if for any reason there is a frequency shift, then the efficiency of operation is decreased.
Furthermore if there is any alteration of the chamber design dimensions, then it will result in an operational compromise.
In addition, since resonant standing waves are required for proper operation, and if these standing waves are changed for any reason and become traveling waves, either continuously or discontinuously or by slight variations around the vicinity of the ports due to phase shifting, then the operation is again compromised. Also where the waves emitted from the diaphragm or piezoelectric transducer become distorted for any reason. For example the wave changes from a sinusoidal wave to a complex wave with harmonics, then these harmonics have to be realized as having a recognizable effect upon the overall efficiency of the pump's operation. There are frequency limitations connected with some of the design features of such pumps that in many instances, these limitations as discussed below could limit the pump's various applications. In general, if the frequency chosen is to low, then size could be a problem, for it is required for efficient operation that within the chamber at least one wave length be given to the chamber dimension. Even if a half-wave length or a quarter-wave length is used as a physical dimension, there are certain disadvantages to these configurations relating to efficiency of operation. If the frequency utilized is too high, then the fluid could absorb the wave energy and attenuate the standing waves thus effecting overall operation. Accordingly this pump design does not provide efficient reliable pump operation under all conditions.
Referring to the Lucas patents, in both patents the theory of operation and so with the basic embodiment of both patents acknowledges the objective of using a gas in the resonant chamber (cavity) and not a liquid, the later of which is not achievable.
The compressors used in both Lucas' patents likewise utilize embodiments which uses standing waves of acoustic pressure for creating nodes which are periodic points of minimum pressure and antinodes which are periodic points of maximum pressure. The standing wave phenomenon of course requires a resonant state for proper operation so as with these compressors of the Lucas patents.
These compressors require that a very narrow resonant operational frequency range be utilized by way of specific electronic control circuitry. This control circuitry includes microprocessor controlled phase locked loops to insure frequency stability, thus adding to the complexity of the design. Such control circuitry is necessary for such a complex compressor system used for refrigeration.
The essence of Lucas' compressors, require the creation of a standing wave within a resonant chamber or cavity, and further attempting to maintain the standing wave with its fixed periodic nodes and antinodes of pressure. These nodes and antinodes are required to be precisely located at the entrance and exit fluid ports. This is done for the purpose of moving a gaseous refrigerant one way into a heat exchanger, where the excess heat generated from compression is carried off and the gaseous refrigerant is thereby cooled to a liquid phase. This cooled liquid is then passed through a volume that contains a number of ingredients to be cooled--such as food, etc. After the heat of the food or whatever, is passed to the liquid, it (the liquid) heats up and expands into the gaseous phase once more; only then to re-enter the resonant chamber of the compressor to begin the cycle all over again. In order to accomplish this task the internal mechanism of the compressor requires a longitudinal standing wave and that such a wave must be transverse to the exit and entrance ports. This mechanism is further established by action of streaming effecting the overall efficiency of such compressors by taking away energy from the wave. This streaming effect occurs when the very same pressure differentials that allow for transverse gaseous flow between exit and entrance ports, are of sufficient amplitude to cause a gaseous flow between the nodes and antinodes within the resonant chamber. This results in a continuous forth and back gaseous flow between the nodes and antinodes and sets up net flow impedance (a complex restriction to fluid flow) to the main flow to the port of ports. Streaming is similar to hydrodynamic eddy currents in fluids or electrical eddy currents in electrical transformers, etc. Decreased efficiency in overall operation is a result of such effect. Since the internal mechanism of these compressors is a longitudinal standing wave and that this wave is transverse to the exit and entrance ports. Accordingly the operation of the compressors is dependent upon the transverse or shear wave component of the standing wave. It is the transverse component, which allows for the initialization of the gaseous flow into the exit port, by means of a wave gradient from the entrance to the exit ports. Another feature of the compressors of Lucas' patents is the use of one or more ultrasonic drivers, which emit periodic ultrasonic energy, which may or may not be linear in nature. It is stated that the frequency of the transducer is above the standing wave frequency. It is then asserted that the energy is demodulated into pulses of complex waves, and that this is accomplished by the higher frequency components being attenuated by the gaseous environment. What is left then, is a pulsed complex wave with lower frequency components; some of which fall into the frequency range of the standing wave frequency and add energy thereto.
Additionally, the Lucas patents states that an ultrasonic transducer can be used in a non resonant pulsed or modulated mode, "non resonant mode" meaning that the frequency of the transducer is not equal to the frequency of the standing acoustical wave. In this pulsed or non-resonant mode, several items need further clarification: the transducer operates at its resonant mode and "that" mode is much higher than the standing wave frequency by design. The transducer is switched on and off to create a succession of short pulses; each pulse consists of a short train of high frequency oscillations. The high frequency components of this pulse train are absorbed or attenuated by the gaseous medium, and the lower frequency components falling within the range of the standing wave frequency will provide the necessary mode of operation. This is in effect overdrives the transducer crystal, creating nonlinear effects and complex waves leading to Fourier components of many frequencies, some of these being that of the standing wave frequency.
It is also suggested that a multiplicity of transducers be placed in contact at the nodes and antinodes, as such placements would allow energy to be added to the standing wave at various points. No doubt, energy would be added, moreover the energy coefficient of transducers is less than unity. The overall effect is like placing a group of transducers in parallel, their energy minus the losses are additive, therefore the same could be accomplished by using one transducer comparable in energy to all of their additive energies.
In view of the above discussion, the following points can be assessed with regard to the devices disclosed by the Mandroian and Lucas art patents:
1. Acoustic standing waves are the primary mode of operation of the prior art. Furthermore the standing waves are increased to their maximum value (taking into consideration system losses) after the generation of a traveling wave from a transducer or other source of acoustic energy. Further, this maximum value assigned to the standing wave is sustained by the constant acoustic energy injected into the system trough the transducer element.
2. A gaseous fluid is the medium of choice for the compressors of Lucas' in order to function properly as a refrigeration compressor.
3. The actual gaseous fluid flow is transverse to the acoustic standing wavefront.
4. Precise geometry of the chamber is essential for successful operation requiring a resonant mode for the chamber; and additional electronic control measures are required to provide frequency compensation circuitry; such as phase locked loops that adjusts for frequency drift above and below the resonant mode of the chamber.
5. The Lucas compressors can utilize a multiplicity of acoustic energy sources situated at any one or all of the acoustic generated pressure nodes and antinodes, for the purpose of feeding additional energy at these points to increase the overall system efficiency.
The prior Deak pump provides an optional ultrasonic transducer arrangement using either a single frequency range or a broadband frequency range using a special design configured transducer, which provide pumping action not requiring a resonant pump chamber, thereby eliminating numerous special arrangements inherent with such resonant pump designs.